Continuously Operating Type Showcase

ABSTRACT

A showcase performs a defrosting process without stopping a cooling process. First and second intermediate ducts are bifurcated from an inflow duct and joined at an outflow duct. A first heat exchanger is mounted inside the first intermediate duct. A second heat exchanger, which is connected to the first heat exchanger, is mounted inside the second intermediate duct. A directional control valve selectively supplies a refrigerant from a condenser into the first heat exchanger or into the second heat exchanger. A fan is installed inside the inflow duct. A first damper is installed between the inflow duct and the first intermediate duct. A second damper is installed between the inflow duct and the second intermediate duct. A control unit controls the directional control valve and the first and second dampers in accordance with a temperature of cool air heat-exchanged with the heat exchangers and a saturation temperature of the refrigerant.

TECHNICAL FIELD

The present invention generally relates to a showcase, and more particularly to a showcase designed for continuous operation by being provided with two heat exchangers, which alternately function as an evaporator for cooling air and as an auxiliary condenser for removing frost by heat of condensation.

BACKGROUND ART

A showcase is an equipment designed to display certain goods at a low temperature in order to slow down the decay of food and other perishable materials (e.g., ice creams, beverages, meats, vegetables, fruits, etc.) stored therein. Thus, the temperature and humidity in a goods-storage room should be properly maintained. The showcase is typically classified into two different compartments, namely, one for cold-storage at about 4° C. and the other for freezing-storage at about −20° C.

An example of a prior art showcase is disclosed in Japanese Patent Publication No. 1999-094442, which will be explained in view of FIGS. 1 and 2. FIG. 1 is a sectional view illustrating an inner structure of a prior art showcase. FIG. 2 is a schematic view illustrating a cooling system of a prior art showcase.

As shown in the drawings, a prior art showcase 1 comprises a main body 10, a goods-storage room 20 whose front portion is opened and an air duct 30 surrounding the goods-storage room 20.

The goods-storage room 20 is equipped with shelves 22 for displaying the goods. An air outlet 24 is provided at the top of the goods-storage room 20, through which the cool air is discharged to form an air curtain (as shown by the arrows depicted in FIG. 1). Further, an air inlet 26 is provided at the bottom of the goods-storage room 20 corresponding to the air outlet 24.

The air duct 30 includes an inflow duct 32 disposed below the goods-storage room 20, an intermediate duct 34 arranged vertically at the rear of the goods-storage room 20, and an outflow duct 36 disposed above the goods-storage room 20. The inflow duct 32 communicates with the air inlet 26, while the outflow duct 36 communicates with the air outlet 24.

A fan 12 is mounted inside the inflow duct 32 for drawing the air in the goods-storage room 20 through the air inlet 26. The fan 12 blows the air toward the intermediate duct 34 and the outflow duct 36. An upstream evaporator 14 and a downstream evaporator 15 are mounted inside the intermediate duct 34. The upstream evaporator 14 is positioned under the downstream evaporator 15.

An accumulator 42, a compressor 44 and a condenser 46 are contained in a housing 40, which is mounted below the main body 10. A first expansion valve 16 is mounted on a conduit 52, which connects the condenser 46 to the upstream evaporator 14. Further, a second expansion valve 17 is mounted on a conduit 54 that connects the condenser 46 to the downstream evaporator 15. Bypass conduits 56 and 58 are branched from a conduit 50 connecting the compressor 44 to the condenser 46. One bypass conduit 56 directly connects the compressor 44 to the upstream evaporator 14, while the other bypass conduit 58 directly connects the compressor 44 to the downstream evaporator 15. A first defrost expansion valve 18 is mounted on the bypass conduit 56, while a second defrost expansion valve 19 is mounted on the bypass conduit 58.

The operation of the above prior art showcase will now be described below.

When the cooling system is started, a gas refrigerant in the accumulator 42 is sucked into the compressor 44, as shown by the solid arrows depicted in FIG. 2. The gas refrigerant is compressed to a high pressure and high temperature in the compressor 44, and is discharged toward the condenser 46 through the conduit 50. The gas refrigerant is condensed into the liquid in the condenser 46.

A portion of the liquid refrigerant in the condenser 46 flows into the first expansion valve 16 through the conduit 52 and is decompressed. Then, the liquid refrigerant flows into the upstream evaporator 14. The other portion of the liquid refrigerant in the condenser 46 flows into the second expansion valve 17 through the conduit 54 and is decompressed. The liquid refrigerant then flows into the downstream evaporator 15. At this time, the first and second defrost expansion valves 18 and 19 are kept in a closed state. The liquid refrigerant is vaporized in the upstream and downstream evaporators 14 and 15, and then the gas refrigerant is returned into the accumulator 42. The gas refrigerant in the accumulator 42 is once again sucked into the compressor 44. The above-described cooling cycle is repeated.

The surface temperature of the upstream and downstream evaporators 14 and 15 falls below the freezing point by the latent heat of vaporization of the liquid refrigerant, thereby cooling the air passing by fins of the evaporators 14 and 15. The cool air is supplied into the goods-storage room 20 and cools or freezes the goods on the shelves 22.

As the cooling cycle continues, the moisture in the air is condensed on the surfaces of the evaporators 14 and 15, thereby generating the frost thereon. The frost reduces the effective contact area between the fins of the evaporators 14 and 15 and the air passing thereby, which deteriorates the cooling efficiency of the showcase. To solve this problem, the defrosting process should be performed periodically. During the defrosting process, the first and second expansion valves 16 and 17 become closed, and the first and second defrost expansion valves 18 and 19 become opened. Accordingly, the hot gas discharged from the compressor 44 is directly introduced into the evaporators 14 and 15 in the direction of dotted-arrows depicted in FIG. 2 via the opened defrost expansion valves 18 and 19, thereby removing the frost on the evaporators 14 and 15.

With the exception of the above defrost method using the hot gas, the so-called off-cycle defrost method and the heater defrost method are used. The off-cycle defrost method is adapted to remove the frost by stopping the operation of the compressor and operating the fan to blow the ambient air toward the evaporators. The heater defrost method is adapted to remove the frost by installing the electric heater near the evaporators and operating the heater to radiate the heat.

However, the aforesaid prior art defrost methods are disadvantageous in that the operation of the cooling system needs to be stopped while the defrosting process is performed. Thus, the temperature in the goods-storage room inevitably rises, which can lead to the spoiling or rotting of foods contained therein. Especially, the off-cycle defrost method has drawbacks since it takes a relatively long time to remove the frost. The heater defrost method has problems in that power consumption for operating the electric heater is increased and significant attention needs to be given to electric insulation. Further, the heated air may soak into the goods-storage room and raise the temperature, even to 20° C., thereby causing decay of food. Further, power consumption for restarting the cooling system to reduce the raised temperature in the goods-storage room is also increased, which causes the costs of maintaining the showcase to rise.

Also, when the frost is so heavy that it cannot be removed by the prior art methods, the operation of the cooling system is completely stopped and the main body of the showcase must be disassembled so as to sprinkle warm water on the frosted evaporators to melt the frost. However, this method may cause the food to decay by the utter stoppage of the cooling process and may require workers for doing such an artificial defrosting process.

DISCLOSURE Technical Problem

It is, therefore, an object of the present invention to provide a showcase designed for continuous operation and can perform a defrosting process without stopping the cooling process.

It is another object of the present invention to provide a showcase adapted for continuous operation, which can reduce power consumption due to the operation of the defrosting process and restarting the cooling process.

Technical Solution

In order to achieve the above objects, the present invention provides a showcase designed for continuous operation and having a goods-storage room for displaying goods at a predetermined temperature, the showcase comprising: a compressor for compressing a refrigerant; a condenser for condensing the refrigerant discharged from the compressor; an air duct for supplying cool air into the goods-storage room; first and second heat exchangers directly connected to each other; an expansion valve disposed between the first heat exchanger and the second heat exchanger; a directional control valve for selectively supplying the refrigerant from the condenser into the first heat exchanger or into the second heat exchanger; air-flow selecting means for selectively causing the air in the goods-storage room to flow toward the first heat exchanger or toward the second heat exchanger; sensing means for detecting a temperature of the refrigerant flowing out of the first and second heat exchangers, a saturation temperature of the refrigerant, and a temperature of the cool air heat-exchanged with the first and second heat exchangers; and a control unit for controlling the directional control valve and the air-flow selecting means in response to the temperature signals from the sensing means.

The air duct includes an inflow duct into which the air in the goods-storage room flows, first and second intermediate ducts bifurcated from the inflow duct, and an outflow duct at which the first and second intermediate ducts are joined and through which the cool air is supplied into the goods-storage room. The first heat exchanger is mounted inside the first intermediate duct and the second heat exchanger is mounted inside the second intermediate duct.

The air-flow selecting means includes a fan installed inside the inflow duct, a first damper installed at a junction between the inflow duct and the first intermediate duct, and a second damper installed at a junction between the inflow duct and the second intermediate duct.

The control unit determines whether a difference between a temperature of the cool air heat-exchanged with the first heat exchanger and a saturation temperature of the refrigerant in the first heat exchanger detected by the sensing means is larger than a predetermined reference value. If the difference is less than the predetermined reference value, then the control unit performs a first operating mode of controlling the directional control valve so that the refrigerant from the condenser flows into the second heat exchanger, opening the first damper, and closing the second damper. If the difference is the predetermined reference value or more, the control unit performs a second operating mode of controlling the directional control valve so that the refrigerant from the condenser flows into the first heat exchanger, closing the first damper, and opening the second damper.

While the second operating mode is performed, the control unit determines whether a difference between a temperature of the cool air heat-exchanged with the second heat exchanger and a saturation temperature of the refrigerant in the second heat exchanger detected by the sensing means is larger than the predetermined reference value. If the difference is less than the predetermined reference value, the control unit maintains the second operating mode. If the difference is the predetermined reference value or more, the control unit stops the second operating mode, but performs the first operating mode.

DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing an inner structure of a prior art showcase.

FIG. 2 is a schematic view showing a cooling system of a prior art showcase.

FIG. 3 is a sectional view showing an inner structure of a continuously operating type showcase constructed in accordance with a first preferred embodiment of the present invention.

FIG. 4 is a schematic view showing an operating state of a cooling system of a showcase constructed in accordance with a first preferred embodiment of the present invention.

FIG. 5 is a schematic view showing another operating state of a cooling system of a showcase constructed in accordance with a first preferred embodiment of the present invention.

FIG. 6 is a schematic view showing an operating state of a cooling system of a showcase constructed in accordance with a second preferred embodiment of the present invention.

FIG. 7 is a schematic view showing another operating state of a cooling valve 116 is mounted on the conduit 150.

A housing 140, which is mounted below the main body 110, contains an accumulator 142, a compressor 144, a condenser 146, a directional control valve 148, a bypass conduit 156, and a flow control valve 149. The compressor 144 sucks the gas refrigerant from the accumulator 142 and compresses the gas refrigerant to a high pressure and high temperature. The condenser 146 condenses the gas refrigerant discharged from the compressor 144. The directional control valve 148 is mounted on a conduit 154 extending from a discharging port of the condenser 146. The directional control valve 148 selects the flow direction of the liquid refrigerant discharged from the condenser 146 toward the first heat exchanger 114 or toward the second heat exchanger 115. The bypass conduit 156 is branched from a conduit 152, which connects the compressor 144 to the condenser 146, and is connected to the conduit 154 extending from the discharging port of the condenser 146. The flow control valve 149 is mounted on the bypass conduit 156 and controls the amount of the refrigerant flowing into the condenser 146 from the compressor 144.

The cooling system of the showcase further comprises sensing means (not shown) for detecting a temperature of the refrigerant flowing out of the first and second heat exchangers 114 and 115, a saturation temperature of the refrigerant, and a temperature of the cool air heat-exchanged with the first and second heat exchangers 114 and 115. The cooling system also comprises a control unit (not shown) for controlling the directional control valve 148, the first and second dampers 138 and 139, and the flow control valve 149 in response to the temperature signals from the sensing means.

The operation of the continuously operating type showcase, which is constructed in accordance with the first preferred embodiment of the present invention, is described below.

When the cooling system is started, a gas refrigerant in the accumulator 142 is sucked into the compressor 144, as shown by the arrows depicted in FIG. 4. The gas refrigerant is compressed to a high pressure and high temperature in the compressor 144. A portion of the gas refrigerant discharged from the compressor 144 flows into the condenser 146 through the conduit 152, and is condensed into the liquid. The other portion of the gas refrigerant discharged from the compressor 144 is directed toward the flow control valve 149 through the bypass conduit 156, and then flows through the conduit 154 extending from the discharging port of the condenser 146. Thus, the gas refrigerant from the compressor 144 and the liquid refrigerant from the condenser 146 are mixed in the conduit 154. Such a gas-liquid mixed refrigerant flows into the second heat exchanger 115 via the directional control valve 148. The second heat exchanger 115 functions as an auxiliary condenser and the gas of the mixed refrigerant is condensed in the second heat exchanger 115. The heat of condensation generated at the second heat exchanger 115 removes the frost on the second heat exchanger 115.

At this time, the flow control valve 149 controls the defrost capacity of the second heat exchanger 115. As the flow control valve 149 becomes opened widely, the amount of the gas refrigerant flowing into the condenser 146 from the compressor 144 is decreased. However, the amount of the gas refrigerant flowing into the second heat exchanger 115 via the flow control valve 149 is increased, thereby enhancing the defrost capacity of the second heat exchanger 115 due to the heat of condensation. On the contrary, as the flow control valve 149 becomes narrowly closer, the amount of the gas refrigerant flowing into the condenser 146 from the compressor 144 is increased. However, the amount of the gas refrigerant flowing into the second heat exchanger 115 via the flow control valve 149 is decreased, thereby decreasing the defrost capacity of the second heat exchanger 115. The flow control valve 149 is controlled by the control unit in response to the signals from the sensing means detecting the temperature of the refrigerant exhausted from the second heat exchanger 115. That is, the control unit adjusts the opening position of the flow control valve 149 in accordance with the difference between the detected temperature of the refrigerant exhausted from the second heat exchanger 115 and a predetermined reference value. If the detected temperature of the refrigerant exhausted from the second heat exchanger 115 (e.g., 35° C.) is less than the predetermined reference value (e.g., 38° C.), it means that the second heat exchanger 115 is in a frost state. Then, the control unit opens the flow control valve 149 more so as to enhance the defrost capacity of the second heat exchanger 115.

The refrigerant, which is condensed while passing through the second heat exchanger 115, flows into the expansion valve 116 through the conduit 150 and is decompressed. Then, the liquid refrigerant flows into the first heat exchanger 114. The first heat exchanger 114 functions as an evaporator so that the liquid refrigerant is vaporized in the first heat exchanger 114. The surface temperature of the first heat exchanger 114 falls below the freezing point by the latent heat of vaporization of the liquid refrigerant, thereby cooling the air passing by fins of the first heat exchanger 114. At this time, the control unit opens the first damper 138 installed at a junction between the inflow duct 132 and the first intermediate duct 134. However, it closes the second damper 139 installed at a junction between the inflow duct 132 and the second intermediate duct 135. Thus, the air in the goods-storage room 120 is drawn into the inflow duct 132 through the air inlet 126 by the fan 112, and cooled while passing by the first heat exchanger 114 in the first intermediate duct 134. The cool air flows through the outflow duct 136 and is supplied into the goods-storage room 120 through the air outlet 124 in an air curtain form (as shown by the arrows depicted in FIG. 3), thereby cooling or freezing the goods on the shelves 122.

The gas refrigerant discharged from the first heat exchanger 114 is returned into the accumulator 142 via the directional control valve 148. The gas refrigerant in the accumulator 142 is sucked again into the compressor 144 and the above-described cooling cycle is repeated.

As the cooling cycle goes on, the moisture in the air is condensed on the surfaces of the first heat exchanger 114, thus generating the frost thereon. If the frost on the first heat exchanger 114 becomes heavy, the control unit operates the directional control valve 148 to change the flow direction of the refrigerant, as shown in FIG. 5. This is when the difference between the detected temperature of the cool air heat-exchanged with the first heat exchanger 114 (e.g., −25° C.) and the detected saturation temperature of the refrigerant in the first heat exchanger 114 (e.g., −45° C.) is considered to be at a predetermined reference value or more. Because the frost reduces the heat-exchanging efficiency between the first heat exchanger 114 and the air passing thereby, the difference between the temperature of the cool air and the saturation temperature of the refrigerant becomes larger as the frost grows heavy on the first heat exchanger 114.

As shown by the arrows depicted in FIG. 5, the gas refrigerant in the accumulator 142 is sucked into the compressor 144, and is compressed to a high pressure and high temperature. A portion of the gas refrigerant discharged from the compressor 144 flows into the condenser 146 through the conduit 152, and is condensed into the liquid. The other portion of the gas refrigerant discharged from the compressor 144 is directed toward the flow control valve 149 through the bypass conduit 156, and then flows through the conduit 154 extending from the discharging port of the condenser 146. Thus, the gas refrigerant from the compressor 144 and the liquid refrigerant from the condenser 146 are mixed in the conduit 154. Such a gas-liquid mixed refrigerant flows into the first heat exchanger 114 via the directional control valve 148. The first heat exchanger 114 functions as an auxiliary condenser and the gas of the mixed refrigerant is condensed in the first heat exchanger 114. The heat of condensation generated at the first heat exchanger 114 removes the frost on the first heat exchanger 114. At this time, the control unit adjusts the opening position of the flow control valve 149 in accordance with the difference between the detected temperature of the refrigerant exhausted from the first heat exchanger 114 and the predetermined reference value. It then controls the defrost capacity of the first heat exchanger 114, as described above.

The refrigerant, which is condensed while passing through the first heat exchanger 114, flows into the expansion valve 116 through the conduit 150 and is decompressed. Then, the liquid refrigerant flows into the second heat exchanger 115. The second heat exchanger 115 functions as an evaporator so that the liquid refrigerant is vaporized in the second heat exchanger 115. The surface temperature of the second heat exchanger 115 falls below the freezing point by the latent heat of vaporization of the liquid refrigerant, thereby cooling the air passing by fins of the second heat exchanger 115. At this time, the control unit closes the first damper 138 installed at a junction between the inflow duct 132 and the first intermediate duct 134, but opens the second damper 139 installed at a junction between the inflow duct 132 and the second intermediate duct 135. Thus, the air in the goods-storage room 120 is drawn into the inflow duct 132 through the air inlet 126 by the fan 112 and cooled while passing by the second heat exchanger 115 in the second intermediate duct 135. The cool air flows through the outflow duct 136 and is supplied into the goods-storage room 120 through the air outlet 124 in an air curtain form (as shown by the arrows depicted in FIG. 3), thereby cooling or freezing the goods on the shelves 122.

The gas refrigerant, which is discharged from the second heat exchanger 115, is returned into the accumulator 142 via the directional control valve 148. The gas refrigerant in the accumulator 142 is sucked again into the compressor 144 and the above-described cooling cycle is repeated.

In the same manner, as the frost becomes heavy on the second heat exchanger 115, when the difference between the detected temperature of the cool air heat-exchanged with the second heat exchanger 115 and the detected saturation temperature of the refrigerant in the second heat exchanger 115 is at the predetermined reference value or more, the control unit operates the directional control valve 148 to change the cooling system to perform the previous cooling mode (see FIG. 4), thereby removing the frost on the second heat exchanger 115.

FIGS. 6 and 7 are schematic views showing the operating states of a cooling system of a showcase, which is constructed in accordance with a second preferred embodiment of the present invention. The components of this embodiment, which correspond to those of the previous embodiment, are indicated by the same reference numerals.

As shown in the drawings, a cooling system constructed in accordance with a second embodiment of the present invention does not have the fan 112 and the first and second dampers 138 and 139 of the previous embodiment (see FIGS. 4 and 5). Instead, the cooling system of this embodiment comprises a first fan 112 a installed at a junction between the inflow duct 132 and the first intermediate duct 134, and a second fan 112 b installed at a junction between the inflow duct 132 and the second intermediate duct 135. Since the other components of this embodiment are identical to those of the previous embodiment, the detailed explanation thereof will be omitted.

As shown in FIG. 6, when the second heat exchanger 115 functions as an auxiliary condenser for achieving the defrost and the first heat exchanger 114 functions as an evaporator, the control unit (not shown) operates only the first fan 112 a installed at a junction between the inflow duct 132 and the first intermediate duct 134. Thus, the air in the goods-storage room 120 is drawn into the inflow duct 132 through the air inlet 126, and is cooled by heat exchanging with the first heat exchanger 114 while passing through the first intermediate duct 134. The cool air flows through the outflow duct 136 and is supplied into the goods-storage room 120 through the air outlet 124 in an air curtain form (as shown by the arrows depicted in FIG. 3), thereby cooling or freezing the goods on the shelves 122. When the difference between the detected temperature of the cool air heat-exchanged with the first heat exchanger 114 and the detected saturation temperature of the refrigerant in the first heat exchanger 114 is at the predetermined reference value or more, the control unit operates the directional control valve 148 to perform the defrosting process on the first heat exchanger 114.

As shown in FIG. 7, when the first heat exchanger 114 functions as an auxiliary condenser for achieving the defrost and the second heat exchanger 115 functions as an evaporator, the control unit stops the first fan 112 a and operates the second fan 112 b installed at a junction between the inflow duct 132 and the second intermediate duct 135. Thus, the air in the goods-storage room 120 is drawn into the inflow duct 132 through the air inlet 126 and is cooled by heat exchanging with the second heat exchanger 115 while passing through the second intermediate duct 135. The cool air flows through the outflow duct 136 and is supplied into the goods-storage room 120. In the same manner, when the difference between the detected temperature of the cool air heat-exchanged with the second heat exchanger 115 and the detected saturation temperature of the refrigerant in the second heat exchanger 115 is at the predetermined reference value or more, the control unit operates the directional control valve 148 to change the cooling system to perform the previous cooling mode (see FIG. 6).

INDUSTRIAL APPLICABILITY

As explained above in detail, a continuously operating type showcase of the present invention is provided with two heat exchangers, which alternately function as an evaporator for cooling air and as an auxiliary condenser for removing frost thereon by the heat of condensation. If the frost becomes heavy on one heat exchanger functioning as an evaporator, the flow direction of the refrigerant and air is changed to convert the heat exchanger into an auxiliary condenser so that the frost on the heat exchanger can be removed by the heat of condensation. Further, the other heat exchanger functioning as an auxiliary condenser is converted into an evaporator. Accordingly, the defrosting process can be achieved without stopping the cooling process, thereby effectively slowing down the rate of decay of food or other perishable materials stored in the showcase.

Also, since the frost can be removed continuously by the heat of condensation, the existent electric heater for defrost is not necessary, thus considerably reducing the power consumption. Further, since it is unnecessary for workers to disassemble the showcase to remove the frost artificially by sprinkling warm water on the frosted evaporator, the maintenance fee of the showcase can be reduced.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes, which come within the equivalent meaning and range of the claims, are to be embraced within their scope. 

1. A continuously operating type showcase having a goods-storage room for displaying goods at a predetermined temperature, the showcase comprising: a compressor for compressing a refrigerant; a condenser for condensing the refrigerant discharged from the compressor; an air duct for supplying cool air into the goods-storage room; first and second heat exchangers directly connected to each other; an expansion valve disposed between the first heat exchanger and the second heat exchanger; a directional control valve for selectively supplying the refrigerant from the condenser into the first heat exchanger or into the second heat exchanger; air-flow selecting means for selectively causing the air in the goods-storage room to flow toward the first heat exchanger or toward the second heat exchanger; sensing means for detecting a temperature of the refrigerant flowing out of the first and second heat exchangers, a saturation temperature of the refrigerant, and a temperature of the cool air heat-exchanged with the first and second heat exchangers; and a control unit for controlling the directional control valve and the air-flow selecting means in response to the temperature signals from the sensing means.
 2. The continuously operating type showcase of claim 1, wherein the air duct includes an inflow duct into which the air in the goods-storage room flows, first and second intermediate ducts bifurcated from the inflow duct, and an outflow duct at which the first and second intermediate ducts are joined and through which the cool air is supplied into the goods-storage room, and wherein the first heat exchanger is mounted inside the first intermediate duct and the second heat exchanger is mounted inside the second intermediate duct.
 3. The continuously operating type showcase of claim 2, wherein the air-flow selecting means includes a fan installed inside the inflow duct, a first damper installed at a junction between the inflow duct and the first intermediate duct, and a second damper installed at a junction between the inflow duct and the second intermediate duct.
 4. The continuously operating type showcase of claim 3, wherein the control unit determines whether a difference between a temperature of the cool air heat-exchanged with the first heat exchanger and a saturation temperature of the refrigerant in the first heat exchanger detected by the sensing means is larger than a predetermined reference value, if the difference is less than the predetermined reference value, the control unit performs a first operating mode of controlling the directional control valve so that the refrigerant from the condenser flows into the second heat exchanger, opening the first damper, and closing the second damper, and if the difference is the predetermined reference value or more, the control unit performs a second operating mode of controlling the directional control valve so that the refrigerant from the condenser flows into the first heat exchanger, closing the first damper, and opening the second damper.
 5. The continuously operating type showcase of claim 4, wherein while the second operating mode is performed, the control unit determines whether a difference between a temperature of the cool air heat-exchanged with the second heat exchanger and a saturation temperature of the refrigerant in the second heat exchanger detected by the sensing means is larger than the predetermined reference value, if the difference is less than the predetermined reference value, the control unit maintains the second operating mode, and if the difference is the predetermined reference value or more, the control unit stops the second operating mode, but performs the first operating mode.
 6. The continuously operating type showcase of claim 2, wherein the air-flow selecting means includes a first fan installed at a junction between the inflow duct and the first intermediate duct, and a second fan installed at a junction between the inflow duct and the second intermediate duct.
 7. The continuously operating type showcase of claim 6, wherein the control unit determines whether a difference between a temperature of the cool air heat-exchanged with the first heat exchanger and a saturation temperature of the refrigerant in the first heat exchanger detected by the sensing means is larger than a predetermined reference value, if the difference is less than the predetermined reference value, the control unit performs a first operating mode of controlling the directional control valve so that the refrigerant from the condenser flows into the second heat exchanger, operating the first fan, and stopping the second fan, and if the difference is the predetermined reference value or more, the control unit performs a second operating mode of controlling the directional control valve so that the refrigerant from the condenser flows into the first heat exchanger, stopping the first fan, and operating the second fan.
 8. The continuously operating type showcase of claim 7, wherein while the second operating mode is performed, the control unit determines whether a difference between a temperature of the cool air heat-exchanged with the second heat exchanger and a saturation temperature of the refrigerant in the second heat exchanger detected by the sensing means is larger than the predetermined reference value, if the difference is less than the predetermined reference value, the control unit maintains the second operating mode, and if the difference is the predetermined reference value or more, the control unit stops the second operating mode, but performs the first operating mode.
 9. The continuously operating type showcase of claim 5 or 8, wherein the showcase further comprises a bypass conduit branched from a conduit connecting the compressor to the condenser and joined to a conduit connecting the condenser to the directional control valve, and a flow control valve mounted on the bypass conduit and controlled by the control unit.
 10. The continuously operating type showcase of claim 9, wherein while the first operating mode is performed, the control unit determines whether a temperature of the refrigerant exhausted from the second heat exchanger detected by the sensing means is less than a predetermined reference value, while the second operating mode is performed, the control unit determines whether a temperature of the refrigerant exhausted from the first heat exchanger detected by the sensing means is less than the predetermined reference value, and the less the temperature of the refrigerant is than the predetermined reference value, the more the control unit opens the flow control valve. 